The report said the rate of dead, disabled and diseased sea turtles discovered in the months following the massive April 20 spill was four to six times above average. The analysis, by the National Wildlife Federation, the Sea Turtle Conservancy and the Florida Wildlife Federation, was conservative and only took into account turtles found on shore, not those rescued or recovered at sea.

Researchers with the federal government said it would take years to determine the full impact of the spill on sea turtles. Necropsies have been done on more than half of 600 turtle carcasses, and while some may have died from oil, most of the turtles drowned in fishing gear, said Monica Allen, a National Oceanic and Atmospheric Association spokeswoman.

Unseasonably cold temperatures last winter were also detrimental to sea turtles, most of which are considered endangered, said Gary Appelson, policy coordinator for the Sea Turtle Conservancy. "Sea turtles have had a tough year,'' Appelson said.